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to, putting fome Calx of tin or Lead, in the exhaufted Receiver of an Air Pump; and apply a Burning Glals, fo as the Focus mall fall on the Calx 5 the Confequence will be a vehement Dilatation of the Calx, from the Centre towards the Circumference^ whereby the Receiver will be broke into a thoufand Pieces. And if a Quantity of any eflential aromatick Oil be pour'd in Vacuo, upon Spirit of Nitre, there will immediately arife a huge Fire, to the great Danger of the By-ftanders.
All the above-mentioned Effects of Elemental Fireva&j be increas'd divers ways, viz.
i°. By Attrition y or a fwift Agitation, or rubbing of one Body againfl another. This is apparent in Solids: A ve- hement Attrition of a Flint, and Steel, every body knows, will produce Sparks. So in Fluids, Cream, by long churn- ing to feparate the Butter, will grow fenfibly warm ; and a Barometer renders the Effect it ill more difcernable. See Attrition.
In effect, all the Heat of an Animal is owing to the A- gitation and Attrition of the Parrs of its Juices againfl: each other, and the Sides of the Veffel. SeeCALiDUM Innatttm.
The more folid, hard, and elaftick the Bodies thus agi- tated are 5 the more Points of Contact they have; the more intenfe the Force whereby they are {truck againft each other, is ; the greater their Motio» ; the quicker the Returns of the Strokes 5 and the longer continued ; the greater is the Heat produced.
Thus, a piece of Spunge rubb'd lightly, and for a little while againfl: another, acquires no icnfible Heat: But a large, heavy piece of Iron brilkly rubb'd againfl: another in a cold Seafon (when Bodies are the denfeft) will prefently acquire an intenfe Heat, fuificient to fire Sulphur, Gun- powder, or the like.
So a Knife whetted brifkly on a dry rough Stone, fhall yield Sparks of Fire; but if Oil, or any other fatty Mat- ter be interpofed, no fenfible Heat mall arife : And the Points of two Needles rubb'd againfl: each other ever fo itrongly, or fo long, will never grow warm ; as only touch- ing in a few Points.
Hence i y , The Globules of theCruor, or red Blood drove by the Force of the Heart againfl: each other, or againfl: the Sides of the Arteries, excite more Heat than the Globules of the Serum, or any other Humor in the Animal. Hence a . Thofe Parts abounding moft in thefe Globules thus agitated, as the Heart, Liver, and Head, will be the hot- teft of all others : And the denfer the Blood, ceteris fari- hus, the greater the Heat, &c. 3 , The quicker the Con- tractions of the Heart are repeated, the greater will the Heat be.
The Second Manner of increajivg the FffeB. of Elemen- tal Fire, is by throwing a Quantity of moift or green Vegetables, cut down while full of Sap, into a large Fleap, and preffing them clofe down : The Refult of which, is, that they grow warm, hot, fmoak, and break out into Flame.
The Third way is, by the Mixture of certain cold Bodies. Thus, Water and Spirit of Wine, firft warm'd, grow much hotter by the Mixture; So, any of the heavy aromatick Oils, as of Cloves, Cinnamon, SafTafras, Guiacum, £5?c. mix'd with Spirit of Nitre, grow exceedingly hot, and burft forth like Vukano's. And the fame may be faid of Spirit of Nitre, and Steel Filings.
The like Effect may be had from dry Bodies. Thus, pure Sulphur, and Steel Filings, well ground and mix'd in equal Quantities, with Water enough to make them into a dry Palle, and laid an Hour or two any where, even under Ground, will fmoak and emit Flame 5 and that with the greaterVchemence, as it is more flrongly prefs'd down. See Earthquake.
The Fourth is by 'PboJpborttSj which is a kind of Magnet, prepar'd from the Parts of Animals, that imbibes and re- tains Fire for many Ages. Sec Phosphorus.
But, in all thefe manners, it does not appear, that any Fire is excited, or generated of what was not Fire before: For, if in a fevere Winter's Day you rub a Plate of Gold brifkly againfl another, they will both grow hotter and hot- ter by Degrees, till at length they become red hot, and at the point of melting : And yet all this time the Plates lofe nothing of their Weight; but fwell or grow bigger in all their Dimenfions.
Hence it follows, that the Particles of the Gold are not converted by the Friction, into Fire; but the Fire exifted before; and all the Effect of the Friction, ££?c. is to collect, or bring together a Quantity thereof before difperfed throughout the Atmofphere.
In Effect, there is no making or producing of Fire de novo. All we can do, is, of infenfible, to render it fenfible, i, e. to collect it out of a greater Space into a leffer- and to direct and determine it to certain Places, This is ef- fected, as above mention'd, by Motion, Attrition, $$c.
The Sun alfo contributes very much to the bringing of Fire to light, by means of his rapid Motion round his Axis ; whereby the fiery. Particles, every where diffufed, are di-
rected and determined in parallel Lines towards certain Places, where their Effect becomes apparent. See Sun.
Whence it is that we perceive the Fire when the Sun is above the Horizon ; but that, when he difappears, his Im- pulfe or Preffion being then taken away, the Fire continues difperfed at large thro' the ethereal Space.
In effect, there is not lefs Fire in our Hemifphere in the Night time, than by day ; only it wants the proper De- termination to make it perceived.
Another way of rendering it fenfible, is, by collecting the parallel Rays into a lefs Com pais, by means of Convex Glaffes, or Concave Specula. See- Lens, Burning Glass,
This Elemental Fire is prefent every where, in all Bo- dies, all Space, and at all Times ; and that in equal Quan- tities : For, go where you will, to the Top of the higheft Mountain, or defcend into the loweft Cavern ; whether the Sun mine, or not ; in the coldeft Winter, or the moft fcorching Summer; by one or other, or all of the means' above mentioned may Fire be collected. In a Word, there is no affignable phyfical Point without Fire; no Place in Nature, where the Attrition of two Sticks will not render it fenfible.
So long as Fire remains equably, and undetcrmin'd in any Place, it does not difcover it felf by any Effect. In the fe- vereft Weather we perceive no Influence or Effect of Fire f when, at the fame time being collected and determined by Attrition, it becomes manifeft.
By changing Fire out of its indeterminate State, and impelling it in converging Lines, its Moment is increafed. Witnefs the Phenomena of Burning Glaffes.
But, how Attrition, crude Vegetables, &c. contribute.tcr- wards altering the Direction, £jc. of Fire, does not appear.
Of this Fire, and the Effects thereof above mentioned, depends all Fluidity of Humours, Juices, &c. All Vegeta- tion, Putrifaction, Fermentation, animal Heat, &c. See Fluidity, Vegetation, Putrefaction, &c.
II. But in what manner foever, Fire is collected in Bo- dies ; upon a Ceffation of the collecting Caufe, it foon dif- appears again, unlefs it be fupphed with, a Pahdum t otV\xGU In which cafe it becomes Culinary Fire. — — -
By Pabulum, or Fnel of Fire, we mean whatever re- ceives, and retains Fire ; and is confumed, or at leaft ren- der'd infenfible thereby. See Fuel.
The only 'Pabulum of Fire, in allNature,is the Oil, Sul- phur, or Fat of Bodies: And Bodies are only Fuel, on ac- count of the Oil they contain.
Hence i°, All Vegetables, not too moift, nor too dry, afford fuch a Pabulum ; particularly thofe, which contain, the greateft Quantity of Oil 5 as Balfamick and Reiinous Woods, &c. z v , All vegetable and animal Coals are a proper Pabulum for maintaining of Fire ; as being only the Parts of Vegetables and Animals, which have exhaled their Water and Salt, and retain'd the Oil alone inhering, in a black Form, in their Earth. 3 , All foffil and bituminous Earths, Turfs, &c. 5 , All Mineral Sulphur, whether pure or join'd with Earth, Stone, or Metals ; as Pit-Coal, &c. <>°,"The Fat and Dung of Animals ; and 7 , Several Pro- ductions of Chymiltry ; as Oils, inflammable Spirits, £5?c.
This Fire, which burns combuflible Bodies, requires Air, to fuftain it ; which taken away, the Fire is immediate- ly diffipated : As appears from the Experiments in Vacuo.
And yet, Fire does not immediately bear, or endure the Air 5 but always repels it: And by that means forms a kind of Vault, or aerial Furnace all round ; which by its Weight, and the Preffiire of the incumbent Air acts on all the Par- ticles, or Corpufcles that would make their Way through it 5 and thus retains the Fire, and applies it to the combuitible Matter.
Hence, the heavier the Air, the more vehement the Fire: And accordingly, in {till cold Weather we oblcrve the Fire to act with more Violence than in warm Weather.
But whether the Air retains Fire by its Weight alone (which Water it felf would do) , may be c|ueftioned : And whether its Elasticity does not contribute iomething there- to; aa alfo, whether there be not fome further unknown Property in the Air, that has a. Share, may be doubted. Something of this kind one would fufpect from hence, that all Air is not proper to maintain Flame. See Air.
This Fire, in burning a combuitible Matter, affords a finning Fire, or a Flame, or both, according to the Diver- fity of Fuel; and frequently, Smoak, Soot and Afhes.
Shining, or luminous Fire, feems to be elemental Fire, attracted towards the Parts of the Sulphur, or Oil, with- fuch Force and Velocity, as to move, and make them very violently, whirl them about, divide, and attenuate them, and thus render them volatile, and ready to be expelled : While, in the mean time, the Air, making its Vault all around, reftrains and keeps them in, directs them to the Sulphur, and keeps them itill collected in their Plate or Pa- bulum, while the combuitible Matter is diffufed al/f around-
Flame
